Isolated magnetostrictive buffered liquid level sensor

ABSTRACT

A magnetostrictive application probe is disclosed wherein the probe includes a preassembled sensor element mounted as an application housing installation as an installable unit. The modular nature allows interchanging with various electronic assemblies, and may be an explosion proof installation.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.08/500,004, filed Jul. 10, 1995 which is a continuation-in-part of U.S.application Ser. No. 08/439,502 filed May 11, 1995, both entitled “LocalBuffer Circuit”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to magnetostrictive displacement ordistance measuring transducers, and more particularly tomagnetostrictive transducers having modular construction including fordisplacement or distance measuring and adapted for easy configuration ofassembly of field equipment after manufacture or assembly from stockedmodules. This construction also facilitates modular construction of anexplosion-proof field device.

2. Description of the Art

Magnetostrictive transducers having elongated waveguides that carrytorsional strain waves induced in the waveguide when current pulses areapplied along the waveguide through a magnetic field are well known inthe art. A typical linear distance measuring device using a movablemagnet that interacts with the waveguide when current pulses areprovided along the waveguide is shown in U.S. Pat. No. 3,898,555.

Devices of the prior art of the sort shown in U.S. Pat. No. 3,898,555also have the sensor element embedded into the protective housing whichalso houses the electronics to at least generate the pulse and providecertain mounting means associated with the device for the customer.

U.S. Pat. No. 5,313,160 teaches a modular design in which the sensor andelectronic assembly can be removed from the application package. In theapplication package is the outer housing which is used by the customerfor mounting an attachment of the sensor and electronics assembly withthe end device whose position is to be measured. Sensor designs of thepast have required delicate handling until the fabrication of the totalunit, including the outer housing and electronics, has been completed.Prior art also utilizes difficult to produce and expensive methods tosuspend the waveguide and to prevent the reflection of the desired sonicstrain wave. Prior high performance waveguide suspension systems utilizethin elastomer spacer discs which are individually positioned along theentire length of the waveguide. Installation of the discs is a timeconsuming, usually manual, operation. The best performing dampingdevices in use utilize molded rubber elements with a central hole. Theseare difficult to mold and time consuming to apply.

The prior art has deficiencies in that the electronics are includedwithin the waveguide suspension device and an expensive means forwaveguide suspension is utilized. The prior art also has deficiencies bynot having modular construction and pre-assembled sensor elements.Further if different sizes are needed, the unit must be removed. But inthe prior art, the sensor and the electronic package were not removableand interchangeable because of the application electronics beingattached.

It is an object of the present invention to provide for an easyconfiguration or assembly of field equipment after manufacture orassembly from stocked modules, including modular construction of anexplosion proof sensor.

It is a further object of the present invention to remotely locate thesensor from the electronics.

SUMMARY OF TE INVENTION

The present invention relates to a modularly constructedmagnetostrictive transducer of the sort set out in U.S. application Ser.No. 08/500,004 filed Jul. 10, 1995, having a modular constructedmagnetostrictive transducer, permitting a pre-assembled sensor element.A sensor cartridge which may be used as an explosion proof probe andwhich is environmentally protected and mechanically strong for directuse in process control applications is disclosed. The outer housing canbe made from any weldable metal, and a sheet of teflon or other plasticcan be added, if needed for chemical resistance. The pre-assembledsensor elements allow easy configuration or assembly of field equipmentafter manufacture or assembly of the sensor element. It also permitspotting for environmental seal and explosion proof construction. Thetransducer would be then a rugged component, and may be equipped withthreading to thread to another explosion proof housing which containsthe mating electronics. For explosion proof configurations, theexplosion proof material is anchored within the housing to be held inplace when exposed to higher pressures.

DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention, reference should be had to the following figures in whichlike parts are given like reference numerals, and wherein:

FIG. 1 depicts a side elevated view of the complete sensing elementassembly;

FIG. 2 a is a cross-sectional view of the sensing element assembly ofthe preferred embodiment of the present invention of FIG. 1 taken alongsection lines 2-2 of FIG. 1 showing a portion of the waveguide andsurrounding sleeves showing the damping element at the end of thewaveguide;

FIG. 2 b is the same cross-sectional view of FIG. 2 a, but showing afirst alternative of using a tuning wire between the damping element andthe waveguide;

FIG. 2 c is the same cross-sectional view as FIG. 2 a, but shows asecond alternative of external tube crimped over the damping element;

FIG. 2 d is the same cross-sectional view of FIG. 2 a, but shows a thirdalternative of the return wire in a different position and with anexternal tube crimped over the damping element;

FIG. 3 depicts an elevated end view of the housing which shows theconnector;

FIG. 4 is a cross-sectional view of the sensing element assembly of thepreferred embodiment of the present invention of FIG. 1 taken alongsection lines 4-4 of FIG. 1 showing the cross-section of the housing anda portion of the waveguide and surrounding sleeves but not showing thedamping mechanism;

FIG. 5 is a plan view of the bracket of the preferred embodiment of thepresent invention;

FIG. 6 is a plan view of the bracket cover of the preferred embodimentof the present invention;

FIG. 7 is a first profile view of the bracket of the preferredembodiment of the present invention;

FIG. 8 is a first profile view of the bracket cover of the preferredembodiment of the present invention;

FIG. 9 is a second profile view of the bracket of the preferredembodiment of the present invention showing it juxtaposed with thebracket cover of the preferred embodiment of the present invention;

FIG. 10 is a third profile view of the bracket of the preferredembodiment of the present invention showing the bracket coverjuxtaposed;

FIG. 11 is a view in profile of the end opposite to the end of FIGS. 9and 10 of the bracket of the preferred embodiment of the presentinvention showing the bracket cover juxtaposed to it;

FIG. 12 is a different side view of the profile of the bracket of thepreferred embodiment of the present invention;

FIG. 13 illustrates a cross sectional view of a sensor assembly usingthe transducer of the preferred embodiment of the present invention;

FIG. 14 illustrates a cross-sectional view of the sensing elementassembly of an alternate embodiment of the present invention of FIG. 1taken along section lines 2-2 of FIG. 1 showing a portion of thewaveguide and surrounding partial sleeves and showing the dampingelement at the end of the waveguide;

FIG. 15 is an elevated view of the sensor cartridge of the preferredembodiment of the present invention;

FIG. 16 is a partial sectional view of a portion of FIG. 15, showing themodularly constructed pre-assembled sensing element amid the potting;and

FIG. 17 is a side view, partly in phantom line, of the isolator/pottingplug of the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A transducer or sensing element assembly of the type disclosed in U.S.application Ser. No. 08/500,004, filed Jul. 10, 1995, the disclosure ofwhich is partially repeated below, or any other modular transducer thatmay be introduced in the future for purposes of permitting theproduction of easily assembled field equipment including explosion prooftransducers, is shown indicated at 25 in FIG. 16. Transducer 25 ispreassembled as a sensing element and may be used for measuringdisplacements and/or distances or other measurements, and the fieldassembled device of the present invention will be applicable to any ofthem. The type of transducer that may be used for the present inventionshould not be considered to be limited by the type of modularconstruction for pre-assembly use with the probe, including thepreferred embodiment described below. The transducer and assembledsensor element should not be deemed to be limited to any particular typeof electronics used with the waveguide. Additionally, the general typeand nature of a transducer in electrically producing the return pulseand interfacing through the return pulse with any electronics of a buyeror user of the device, except that it be pre-assembled, should not bedeemed to be limited by the disclosure.

The type of transducer that may be used for the present invention,should not be considered to be limited by the disclosure of the dampingelement used with the transducer Further, except for mechanicalconstruction indicating a preferred mechanical mounting of thewaveguide, the general type of transducer should not be deemed to belimited by the disclosure of the waveguide suspension. The transducershould not be deemed to be limited to any particular type of electronicsused with the waveguide except for the local buffer circuit.Additionally, the general type and nature of a transducer inelectrically producing the return pulse and interfacing through thereturn pulse with any electronics of a buyer or user of the deviceshould not be deemed to be limited by the disclosure except for themechanical construction shown for the preferred embodiment and theprinted circuit board containing the local buffer circuit.

The transducer 25 includes an elongated waveguide assembly enclosed inan enclosure tube 3. Enclosure tube 3 and the waveguide assembly aremechanically supported at one end by a housing 17 through an end flange19. The waveguide assembly includes the outer enclosure tube 3surrounding a coaxial elongated interior waveguide 4 (FIG. 2). whenever“FIG. 2” is referenced in this specification, it means any of theembodiments of FIGS. 2 a-2 d. A current is passed through the waveguide4 and returns through a return wire 1 electrically connected to thewaveguide 4. Typically, a magnet (not shown) is mounted over thewaveguide assembly and enclosure tube 3 by being placed over and coaxialwith enclosure tube 3. The magnet interacts with the current pulse asmore completely described in U.S. Pat. No. 3,898,555. Upon the strainwave pulse returning to the housing 17 after passing through thewaveguide 4 and return wire 1, the placement of waveguide 4 and returnwire 1 being more completely described below, a suitable mode converter(partially shown) of any type known or to be known in the art providesan electrical signal through connector 21 to any electronic circuitconnected to it, such as electronic circuit 26.

The structure of the circuit 26 is dependent on the use of transducer25, and will work with the waveguide suspension sleeve 2 and modularconstruction elements of the present invention despite disparities instructure. The structure of circuit 26 should not be considered aslimiting the invention. Thus, no particular mechanism for thearrangement of the element 26 or any conditioning of the signal tocircuit 26 is shown to be preferred to emphasize generality. Further, itshould be understood that the waveguide suspension sleeve 2 mechanism ofthe present invention is applicable to any transducer 25 and waveguide 4of the type for measuring displacement and/or distance and/or othermeasurement using the magnetostrictive principles, such as generallyshown in U.S. Pat. No. 3,898,555, but is dependent for modular assemblyto some extent on the mechanical arrangement of elements in housing 17.Thus, for example, a particular mechanism for a preference for thearrangement of the elements in the housing 17 is shown to be preferredfor mounting, but otherwise should not limit generality. The mechanismother than mounting may be of any sort, including such as those shown inU.S. Pat. No. 3,898,555 or others known in the art or still to bethought of in the art or that are in design in the art. For this samereason the type of magnet used and the type of application used is alsonot shown, and may be any application. Finally, because there is someneed to show the interaction between the damping element 6 FIG. 2) andthe waveguide suspension sleeve 2 and other portions of transducer 25 atthe remote portion of the waveguide assembly, a preferred embodiment foran enclosure tube 3 (FIG. 2), discussed below, with the waveguidesuspension sleeve 2 and damping element 6 is shown. This should not beconsidered as limiting but only illustrative, the waveguide suspensionsleeve 2 being capable of use with any type of waveguide assembly as setout above.

The remote end portion of enclosure tube 3, remote from housing 17, isshown in cross-section in FIG. 2 and ends with an end plug 20. An inertgas may be introduced in enclosure tube 3 to further promote isolationand sealing. End plug 20 acts to stop fluid and other materials fromentering enclosure tube 3. The end of the waveguide assembly having endplug 20, is normally the end which would be at the bottom of a tank, iftransducer 25 is being used for determining the level of liquid in atank, or at the end of the displacement if the transducer 25 were usedto measure distance. As discussed in the Background, it is desired tomake the dead zone, or non-signal producing zone, adjacent to the endplug 20 as short as possible and yet accomplish the purpose of dampeningthe sonic strain wave signal to prevent reflected strain waves frominterfering with the desired return strain wave signal that representsdistance or level, such as discussed in U.S. Pat. No. 3,898,555.

As shown in FIG. 2, a waveguide 4 is enclosed through concentricallylayered enclosure mechanisms, including a suspension sleeve 2 andenclosure tube 3. The suspension sleeve 2 comprises a tubular braidedsleeve, or elastomer sleeve, or composite sleeve, of a geometry havingthe characteristics of restricting the lateral movement of the waveguide4 and insulating the waveguide 4 from vibration and external sonic noiseyet not contacting the waveguide 4 so much as to damp the sonic strainwave signal generated by the interaction of the electric current andexternal magnet. Suspension sleeve 2 is coaxial with and surrounds thewaveguide 4 for substantially its entire length, or at least a majorportion thereof Suspension sleeve 2 is shown mounted within and coaxialfor substantially the entire length of waveguide 4, or at least a majorportion thereof, with outer enclosure tube 3.

The inner diameter of the suspension sleeve 2 must be small enough tolimit the movement of the waveguide 4 yet large enough so that it doesnot hold, grab, constrict or otherwise compress the waveguide 4. Ifsuspension sleeve 2 compresses, holds, grabs or constricts the waveguide4, attenuation of the sonic strain wave signal along waveguide 4 willoccur. The Wiedemann Effect does not promote a large sonic strain wavesignal in the prior art, making it difficult to differentiate it fromnoise produced by other mechanisms. Accordingly, signal attenuation isknown in the prior art to be a phenomenon to be avoided.

The outer diameter of suspension sleeve 2 must be large enough torestrict lateral movement of suspension sleeve 2 within enclosure tube3, yet small enough to fit easily within the inner diameter of theenclosure tube 3, together with the return wire 1 as will be discussedbelow. Also, it may be possible to have the suspension sleeve 2 presentwithout requiring the restriction of an enclosure tube 3, and the use ofan enclosure tube 3 should not be considered limiting to the inventionor even to the waveguide suspension. Overall, the waveguide 4 must besuspended in a manner that cushions it from shock and vibration stimuliso that associated erroneous responses are eliminated.

Suspension sleeve 2 includes an inner layer 27 and an outer layer 29.The fiber that makes up inner layer 27 of suspension sleeve 2 isnonconducting and may be a fine, hard material, or a combination ofmaterials such as ceramic or glass or metal or polymer. The strand countand weave configuration of such fiber are typically from eight tosixteen strands in diamond, regular, hercules or other weave pattern.Such strand, count and weave configuration enable the suspension sleeve2 to act as a cushion between the waveguide 4 and the enclosure tube 3.Interior to the inner layer 27 and exterior to the waveguide 4, there isclearance 28 such that the inner layer 27 is loosely fitting aroundwaveguide 4. The outer layer 29 of suspension sleeve 2 helps to maintainthe shape of the inner layer 27, and isolate it from the enclosure tube3. The outer layer 29 is typically a softer material, such as a siliconerubber and is a second layer of inner layer 27.

Suspension sleeve 2 ends at its remote side at end 31 facing toward theend plug 20, Juxtaposed with the end 31 of the suspension sleeve 2 isdamping element 6. Damping element 6 is slipped over the end of thewaveguide 4 and is coaxial with waveguide 4 and generally cylindrical inshape, as is suspension sleeve 2. However, the damping element 6 is notloose fitting over the waveguide 4, but is more constrictive overwaveguide 4 in order to provide damping. Thus, as shown in FIGS. 2 a and2 b, the inner layer 27 of damping element 6 snugly fits about waveguide4. Further, the outer layer 29 of damping element 6 while usually ofsofter elastomer materials, such as silicone rubber, does not normallycontact enclosure tube 3, as does outer layer 29 of suspension sleeve 2,but instead is sized to control the amount of and to exert pressure onthe inner layer 27 which in turn exerts pressure on the waveguide 4.Thus, a space is left between the outer layer 29 of damping element 6and the inner surface of enclosure tube 3.

In addition, a tuning wire 5 (see FIG. 2 b) of a diameter ranging from0.005 inches to 0.016 inches may be used to act as a wedge, therebycontrolling the pressure of inner layer 27 on the waveguide 4. Thetuning wire 5 is adjacent to waveguide 4 and extends substantially alongand is enclosed by inner layer 27 of damping element 6. It is used tochange the acoustic impedance of the damping element 6 but to do sogradually so that the sonic strain wave signal is dampened graduallyalong the distance of the waveguide 4 enclosed by damping element 6. Inthis way, no reflection will occur from sudden changes in impedance, butinstead damping of the sonic strain wave amplitude along the dampingelement 6 will occur. It should be noted that the tuning wire 5 whileonly shown in FIG. 2 b may be used with any of the configurations ofFIGS. 2 a-2 d and may be used in any other kind of damping element forthe purposes set out above.

Further, because damping element 6 is used to provide optimum damping ofthe sonic strain wave pulse traveling in the waveguide 4, and becauseproper acoustic matching of the waveguide 4 and the damping element 6 isdetermined by the pressure exerted on the waveguide 4 by the inner layer27, there are other mechanisms besides the tuning wire 5 that can beused. As shown in FIGS. 2 c and 2 d, a damping element 6 for use over abroad temperature range could be used, comprising a short braided sleeve8 of the sort of inner layer 27, but with such braided sleeve 8 insertedinto a coaxial larger diameter metal sleeve 9. This assembly of sleeves8, 9 is slipped onto the end of the waveguide 4. The metal sleeve 9 maythen be crimped such that the braided sleeve 8 contacts the waveguide 4with sufficient pressure to provide the required damping action.

Thus, as seen through FIGS. 2 a-2 d, damping may occur through thepressure of outer layer 29 or through the tuning wire 5 trapped in innerlayer 27 or through the crimping of metal sleeve 9 or by any othermechanism that applies the appropriate pressure to control the impedancematching along a predetermined length of the damping element 6 asdetermined by experiment.

The end 32 of damping element 6 facing end 31 of suspension sleeve 2 ispreferably cut between a 40° and 50° angle and preferably about a 45°angle in order to properly match its impedance at that of the waveguide4.

An additional way to minimize end reflections from the damping element 6is to place another damping sleeve 33 of dissimilar material or size orpressure in front of damping element 6 (toward the suspension sleeve 2).Damping sleeve 33 should be designed to have a closer acoustic impedancematch to the waveguide 4. That is, it should have less pressure, orsmaller outer diameter, or lower mass density than damping element 6, orif it is an elastomer, it should have a low durometer, such that thefront end reflection is minimized. Damping sleeve 33 includes a face 34facing toward face 32 of damping element 6. Face 34 normally has a planesubstantially perpendicular to the longitudinal axis of the waveguide 4.It should be noted that damping sleeve 33 may be used with any of thedamping elements 6 of FIGS. 2 a, 2 b, 2 c and 2 d, and the depictionshowing it only in FIG. 2 a should not limit its generality. Further,the orientation of face 34 will not change if damping sleeve 33 is usedwith the damping sleeves 6 of FIGS. 2 b, 2 c or 2 d, each of which has aslanted face 32. The face 34 will continue to have a plane substantiallyperpendicular to the longitudinal axis of the waveguide 4. Generally,this damping sleeve 33 does not damp as efficiently as the dampingelement 6, but it will damp the reflection from the damping element 6,thereby lowering the overall sonic energy leaving the damping system,damping element 6 acting as the primary damp and damping sleeve 33acting as a secondary damp.

Still another method of minimizing the front end reflection coming fromthe damping element 6 is to expand the inside diameter of the dampingelement 6 at the front end. The end facing suspension sleeve 2. This canbe accomplished by inserting a flaring tool in such front end of thedamping element 6 just prior to placing it on the waveguide 4.

Still another method for minimizing the front end reflection coming fromdamping element 6 is to remove material from the outside diameter onsuch front end of damping element 6. This removal region should be inthe range of 0.125″ to 0.5″ as measured from such front end of dampingelement 6. This can be accomplished, for example, by using a set of wirestrippers to remove part of the elastomer that overlaps the braid.

The return wire 1 must pass over damping element 6 as shown in FIGS. 2a, 2 b and 2 d, or through damping element 6 as in FIG. 2 c. In FIG. 2c, the return wire 1 is insulated (as it may be in all other cases) andcan also act in a manner similar to the tuning wire 5 of FIG. 2 b. Inall events, the return wire 1 must then be attached to the tip of thewaveguide 4 using solder or a crimp ring 7, and must be electricallyconnected to form the rest of the circuit to support the current pulsewhich begins in housing 17 and flows through waveguide 4 to returnthrough return wire 1, which may be arranged as discussed in U.S. Pat.No. 3,898,555 or any other way known or to be known in the art.

The pressure applied by the inner layer 27 may be substantially uniform,but may also be nonuniform with less pressure on the side facing thehousing 17 and more pressure on the side facing the end plug 20 toshorten the length of the damping element 6 for a given dampingeffectiveness while preventing reflection.

Alternately, the return wire 1 may be braided into suspension sleeve 2or enclosure tube 3 may be conductive and the return wire 1 may beconnected electrically to enclosure tube 3. Otherwise, in assembly, thereturn wire 1 and suspension sleeve 2 are inserted into enclosure tube3. The waveguide 4 is then pulled into the suspension sleeve 2 becausesuspension sleeve 2 is sized such that the waveguide 4 is in loosecontact with it but does not allow excessive lateral movement. Further,the damping element 6 is then slipped over the waveguide 4.

Further, a series of short suspension sleeves 2 may be located along thelength of waveguide 4, instead of a single continuous suspension sleeve2, as shown in FIG. 14, although this is an alternate embodiment andbelieved to be more difficult to construct. In such a series, careshould be taken in the spacing to decouple or otherwise suppressexternal or internal mechanical noise.

Return wire 1, suspension sleeve 2, enclosure tube 3 and waveguide 4 aresupported in housing 17 by a bracket 10 FIG. 4) preferably made ofplastic. The details of the bracket 10 are shown in FIGS. 5-12. Bracket10 includes a base 60, the outer diameter of base 60 being substantiallyequal to the inner diameter of the main enclosure 62 of housing 17. Base60 includes two flanges 64, 66 located on either side of a recessportion 68 of base 60. This arrangement permits a groove 70 (FIG. 4) tobe present between the two flanges 64, 66. A seal ring 16 is locatedinside groove 70 sealingly engaging the sidewalls 72, 74 of flanges 64,66, respectively, and the outward facing wall 76 of recess 68, as shownin FIG. 4. As used above, the word “diameter” does not imply a circularshape. As best seen in FIG. 4 and from the shape of flanges 64, 66, theinterior 62 of housing 17 is more rectangular in shape with two curvedopposing sides. Thus, with the shape and sizing of flanges 64, 66, sealring 16 also contacts the interior sidewall surface 78 of the mainenclosure 62 of housing 17. Therefore, seal ring 16 acts to seal wiringand connectors interior in housing 17 to surface 80 of flange 66 FIG. 4and FIG. 9).

The end of housing 17 is closed by flange 19. An opening 82 is formed inflange 19 and sized to permit enclosure tube 3 to snugly fit throughopening 82 and extend into an opening 84 formed in flanges 64, 66 andrecess portion 68 of base 60 which is coaxial with opening 82 and of thesame size as opening 82. Base 60 also includes a second opening 86formed adjacent to flange 66 and coaxial with opening 84 but of smallerdiameter than opening 84, thereby forming a shoulder 88 between openings84, 86 against which abuts end 90 of the combination of suspensionsleeve 2 and enclosure tube 3.

Bracket 10 further includes an extension 91 that extends beyond base 60toward the end surface 92 of enclosure or housing 17. Extension 91includes an intermediate opening 94 spaced between opening 86 and theend surface 96 of bracket 10 and end 98 of bracket 10. Opening 94 iscoaxial with openings 84, 86. Opening 94 is also partially formed bybracket cover 14 (FIG. 8). In forming such opening 94, a lateral opening100 is formed by the clearance between bracket 10 and a notch 61 inbracket cover 14. Opening 100 connects the interior between opening 94and opening 86 with a channel 30, formed in bracket cover 14.

With the combination of suspension sleeve 2 and enclosure tube 3abutting or otherwise terminating at shoulder 88, both the return wire 1and the waveguide 4 extend from end 90 into the space interior tohousing 17. Return wire 1 is caused to pass through opening 100 and intochannel 30 with a specific alignment described below. Waveguide 4continues coaxial with opening 94 and is anchored by a waveguide anchor11, preferably made of brass. Waveguide anchor 11 has a cylindricalshaped lower end 101 of diameter sufficient to fit into opening 94. Alarger substantially rectangular cap 103 forms the top of waveguideanchor 11 with shoulder 105 formed therebetween. Shoulder 105 rests onsurfaces 102, 104 which form the upper or inner facing surface ofopening 94. Another opening 55 is provided in extension 91 whose axis isat right angles to the axis of openings 84, 86, 94 FIG. 10). Theidentical opening 55 is formed in the other side of the extension 91 asshown in FIG. 7. The waveguide anchor 11 is sized such that in itsseated position with surface 105 in contact with surfaces 102, 104,anchor 11 does not extend over opening 55. Waveguide anchor 11 furtherincludes a central opening 106 coaxial with the axis of suspensionsleeve 2 and waveguide 4. Opening 106 is sized to permit the insertionof waveguide 4 through it.

Cylindrical shaped elements 108, 110 extend from surface 98 and facetoward the end 92 of housing 17. The upper surface 114 of cylindricalmember 110 is substantially coplaner with the end surfaces 96 and act assupports for a printed circuit board 12 mounted near end 92. Cylindricalshaped elements 108 extend from surfaces 96 and engage reciprocallylocated features (not shown) in circuit board 12 to locate and aligncircuit board 12. Printed circuit board 12 is equipped with a series ofopenings 116, 118 and two not shown to permit return wire 1 to passthrough opening 116 and waveguide 4 to pass through opening 118 and twoadditional leads from a pickup coil 13 yet to be discussed. In addition,printed circuit board 12 has openings 120 that permit leads 50 to passfrom connector 21 through printed circuit board 12. Thus, return wire 1,waveguide 4, a dummy lead 50 and leads 35 of pickup coil 13 (yet to bediscussed) all pass through printed circuit board 12 and areelectrically connected by printed circuit board 12 with electricalconnector 21 as five leads 50 (FIG. 3). Connector 21 physically rests onprinted circuit board 12 and extends from it through an opening 122formed in the end 92 of housing 17 to make connector 21 available tocustomers or users as shown in FIG. 3. Housing 17 is closed by flange 19which may also include extensions 124 having openings 126 therethroughfor mounting housing 17 in the customer's or user's device.

As shown in FIG. 7, two additional openings 128, 130 are included inextension 91 of bracket 10. The axis of each opening 128, 130 isperpendicular to the axis of the other openings discussed above. Opening128 is larger than opening 130 and is sized to admit a pickup coil 13(FIG. 4). Pickup coil 13 may be any type coil and is shown preferablywith a high wire winding count but may be of any design without limitingthe generality of the invention. The pickup coil 13 is shown in FIG. 4as having copper windings 40 mounted on a bobbin base 45. Two leads 35extend from pickup coil 13 through printed circuit board 12 where theyare electrically connected as discussed above. Pickup coil 13 is mountedcoaxially about a tape 15 reciprocally mounted in an opening 132 inpickup coil 13. Tape 15 extends from substantially the end of bobbin 45facing outward towards housing 17 through the pickup coil 13 and to thewaveguide 4 where it is connected to waveguide 4 by welding or othermethod of mechanical connection. Tape 15 does extend for a length 15′beyond the end of the bobbin 45. This length 15′ provides constructiveinterference to the signal. The signal is developed as a voltage acrossthe coil 13. The constructive interference is produced by the sonic wavecontinuing past the coil 13, reflecting from the end of tape 15,including all of the length 15′ and arriving back at coil 13 with suchtime delay as to produce an additive effect. This causes constructiveinterference for any type of tape 15 or circuitry with respect to thecoil 13. An anchor or bracket for the end of tape 15 could alternatelybe used to set the length 15′. Tape 15 is typically made of aferromagnetic or magnetostrictive material and may be of the samematerial as the waveguide 4 but have a different metallurgicaltreatment. Opening 128 is thus located in close proximity to channel 30to place the pickup coil 13 in close proximity to return wire 1, therebypermitting a reduction in energy of the input pulse to waveguide 4.

Opening 130 is sized to receive a bias magnet 18 or unmagnetized magnetmaterial which could be installed for later magnetization during theassembly process.

For assembly of the waveguide assembly into housing 17, the waveguide 4is placed into the waveguide anchor 11 after suspension sleeve 2,waveguide 4 and enclosure tube 3 had been inserted into the openings 82,84 of flange 19 and bracket 10. After the waveguide 4 is inserted intoanchor 11, it is connected to the printed circuit board 12. Thesuspension sleeve 2 and enclosure tube 3 are held in place in thebracket 10 with adhesive or by suitable retaining elements not shown.

After the waveguide 4 is placed into the brass waveguide anchor 11 andconnected to the printed circuit board 12, the pickup coil 13 is added.The return wire 1 is held in place while the bracket cover 14 isinstalled and then the tape 15 is welded or otherwise mechanicallyconnected onto the waveguide 4 using openings 55. It is not necessary toattach the tape in the sequence set out above and the sequence shouldnot be considered as limiting for all the inventions disclosed. The biasmagnet 18 is then installed, or as indicated above unmagnetized magneticmaterial could have been installed earlier and then magnetized. Finallyseal ring 16 is placed into groove 70 of bracket 10. Thereafter, thebracket 10 and the waveguide 4 and the flange 19 (if the flange 19 isused) as an assembly is inserted into the housing 17. The housing 17 iscrimped and/or welded in place. Finally, the air inside the device isdisplaced by a dry, unreactive gas, and the end plug 20 is held in placewith adhesive or other means.

The distance and location of return wire 1 with respect to waveguide 4can be adjusted in any appropriate manner to permit the magnetic fieldsinduced in these two wires to cancel each other. In addition, byproperly routing return wire 1 in the area immediately adjacent the pickup coil 13, the ringing of the interrogation pulse can be reducedsignificantly, such as fifty percent or more. The size and magneticproperties, such as using copper of the sizes set out above for tuningwire 5 also have an effect on the ringing.

Transducer 25 is produced in one inch incremental lengths or some otherincremental length on the order of one-half inch to four inches. This isdone to reduce the total number of unique lengths to which waveguide 4,suspension sleeve 2, return wire 1, and enclosure tube 3 must be cut.This reduces the cost and complexity of manufacturing transducer 25,yielding a more cost effective product. Complete sensor assemblies whichutilize transducer 25 can be manufactured in any length or incrementallength desired. This is accomplished by providing a mounting means fortransducer 25 within the complete sensor assembly which allowstransducer 25 to be positioned axially at any point within ± 1/2 inch ofits median position within the complete sensor assembly. A transducer25, the length of which is within ±½ inch of the length desired for thecomplete sensor assembly, can thus be positioned within the completesensor assembly to provide precisely the sensing length desired.

FIG. 13 illustrates one possible implementation of the mounting meansfor using transducer 25 in one inch incremental lengths (or some otherincremental length on the order of one-half inch to four inches) toproduce sensor assemblies 158 in any length desired. Sensor assembly 158includes an application housing 150 having an endcap 155. Transducer 25is secured to application housing 150 using screw fasteners 152 passingthrough openings 126 of extensions 124 of mounting housing 17 or othersuitable attachment means. When necessary to achieve a proper fit, aspacer block 151 maybe positioned between transducer 25 and applicationhousing 150. Spacer block 151 is utilized in a variety of thicknesses oris not used at all depending on the sensing length required of sensorassembly 158 and the standard length of the enclosure tube 3 containingwaveguide 4 supplied as part of transducer 25. Fasteners 152 are alsoused in a variety of lengths to correspond to the thickness of spacerblock 151. Transducer 25 is shown in FIG. 13 in the middle of the rangeof movement possible within endcap 155. Wire harness 156 carries signalsand supply voltages between transducer 25 and customer or vendorsupplied electronic circuit board 157. Wire harness 156 is of sufficientlength and flexibility to allow transducer 25 to be secured anywherewithin the allowed range of positions after being connected toelectrical connector 21. Electronic circuit board 157 (FIG. 13) providesthe interrogation and signal conditioning circuitry, as known in theart, necessary to communicate with the end user system and to providethe desired position feedback signals. A wire harness 153 is connectedto the electronic circuit board 157 (FIG. 13) and carries signals andsupply voltages between electronic circuit board 157 (FIG. 13) and anexternal connector 154 attached to endcap 155. External connector 154provides the physical means for connecting to the end user system (notshown).

All of the features of a particular preferred embodiment of thewaveguide assembly are not shown in the above disclosure in order toemphasize the generality of the disclosure. For example, a buffercircuit may be used to prevent coil saturation of pickup coil 13 whenthe pulse is initially introduced along waveguide 4. Such a circuitwould help more closely couple the tape 15 and coil 13 to the waveguide4.

Further, the transducer disclosed in this application may be fullyelectrically isolated or shielded including electrically shielded byhousing 17 from all devices in which it is mounted by having mounting orspacer block 151 and screw fasteners 152 made of nonconducting materialand having an insulating material 200 between tube 3 and externalextension tube 202.

The transducer 25 assembled as a sensor element is enclosed in a sensorcartridge 350 which is an application package as an installable unit andincludes an elongated waveguide assembly. Because of the modular natureof the assembled transducer 25, the sensor element 25 may haveinterchanging with various electronic assemblies, and can be used in oras an explosion proof housing. The waveguide assembly is enclosed in anenclosure tube 3 which passes through a cylindrical opening 370 formedby walls 371 of isolator/plug 310. Walls 371 are enclosed by an opening375 formed in a thick front end section 340 of cartridge 350.

Enclosure tube 3 is enclosed in a sheath 300 inserted into an opening360 of front end section 340 which abuts and is coaxial with opening375. Front end section 340 is thick to permit adequate alignment ofsheath 300 and ease of welding. An RTD (not shown) may also be enclosedby enclosure tube 3 from which RTD wires 320 extend from such RTD.Enclosure tube 3 and the waveguide assembly are mechanically supportedat one end by a housing 17 mechanically connected to the waveguideassembly which as set out above, is supported by tube 3 extendingthrough the end of isolator/plug 310 which abuts the end surface ofhousing 17. Opening 370 is sized to permit enclosure tube 3 to snuglyfit through the opening 370. Isolator/plug 310 is not attached to thickfront end section 340 but merely has walls 371 inserted into opening375. End 372 of isolator/plug 310 abuts interior end wall 335 of thickfront end section 340. If potting material is used for explosion proofapplications, the potting material, as discussed below, will hold theisolator/plug 310 in place. Otherwise, isolator/plug 310 would beattached to 340.

The waveguide assembly includes the outer enclosure tube 3 surrounding acoaxial elongated interior waveguide. Typically, a magnet (not shown) ismounted on the sheath 300 by being placed over and coaxial with sheath300. The magnet interacts with a current pulse as more completelydescribed in U.S. Pat. No. 3,898,555. The type of magnet used and thetype of application used is not shown, and may be any application.

The end portion of enclosure tube 3, that is remote from housing 17, isshown in cross-section in FIG. 16 and ends with an end plug (not shown).Sheath 300 extends beyond the end of enclosure tube 3 and ends with anend plug 330. An inert gas may be introduced in enclosure tube 3 tofurther promote isolation and sealing. End plug 330 acts to stop fluidand other materials from entering enclosure tube 3.

Enclosure or housing 17 is located in a cylindrical opening in theinterior of sensor cartridge 350. Opening 380 extends interiorly frominterior wall 335 to opposing end 381. Enclosure 17 extends intointerior 380 from the interior facing wall 382 of isolator/potting plug310 to the interior face 381 of threaded end 420 of sensor cartridge 350which contains exit conduit or cable jacket 390. RTD wires 320 extendfrom isolator/potting plug 310 through the interior 380 of sensorcartridge 350 and through exit conduit oer cable jacket 390. Conductors156 extend from housing 17 through the interior 380 of sensor cartridge350 and through exit conduit 390. Exit conduit 390 may include, and forexplosion proof installations would include, strain relief ring 400 toremove the possibility of the customer pulling out the cable.

For explosion proof installations, the interior 380 of sensor cartridge350 is filled with a potting compound 410, such as SYLAST 2651 withCatalyst #9, for an explosion proof seal. The interior of the end 420 ofsensor cartridge 350 is filled to face 381 with a waterproof pottingcompound from which extends conduit 390. End 420 is threaded by threads430 adapted to be attached to a user housing (not shown) containingappropriate electronics.

Threads 470 terminating at cut back 490 are formed in interior 380 ofsensor cartridge 350. Threads 470 and cut back 490 are formed adjacentto end 471 of the main body portion of sensor cartridge 350. The threads471 and cut back 490 should be of sufficient depth to hold the waterproof potting compound 410 in place so that it cannot be forced out,such as around exit conduct 390 by pressure applied through the process,such as through sheath 300.

Detents 450 are formed in the external portion of the main body ofsensor cartridge 350 to facilitate screwing the body portion of sensorcartridge 350 into an exterior explosion proof housing (not shown) whichmay also be explosion proof.

Because many varying and different embodiments may be made within thescope of the invention concept taught herein which may involve manymodifications in the embodiments herein detailed in accordance with thedescriptive requirements of the law, it is to be understood that thedetails herein are to be interpreted as illustrative and not in alimiting sense.

1. A probe for isolating a magnetostrictive sensor adapted for detectingand measuring the level of liquid in a container, from signal processingcircuitry, the signal processing signals from the sensor; comprising: asignal conditioner having a buffer circuit to condition the signalprocessing signals to a buffered signal; a housing enclosing said signalconditioner and having an exterior and interior; first means formounting said signal conditioner and the sensor in said interior of saidhousing, including the adaptation for detecting and measuring the levelof liquid; and a second means for permitting the signals from thebuffered sensor to be sent to the signal processing circuitry exteriorto said housing.
 2. The probe of claim 1, wherein there is furtherincluded a conduit, said conduit mounted in said interior of saidhousing opposite the buffered circuit, said conduit extending from saidinterior of said housing to the signal processing circuitry.
 3. Theprobe of claim 8, wherein the sensor includes wires located in saidinterior of said housing, said wires extending interiorly from thebuffered circuit through said conduit.
 4. The probe of claim 1, whereinthe sensor includes a transducer having modular portions.
 5. A probehaving one or more features describe in the specification.